The present invention relates to an image recording apparatus for recording an image on an image recording medium and to a sheet cartridge assembled in the image recording apparatus and accommodating therein the image recording medium.
Various types of image recording apparatus have been known for recording an image on an image recording medium. Among these, one conventional image recording apparatus employs an elongated web-like image recording medium which is rolled and accommodated in a sheet cartridge. The image recording medium comprises a photosensitive recording medium, and therefore, the sheet cartridge per se is normally maintained in light-shielded fashion. When installing the sheet cartridge into the image recording apparatus, the elongated photosensitive recording medium is pulled out of the cartridge and the medium is installed on a predetermined sheet path of the apparatus and is wound over a takeup shaft.
When the image recording medium in the cartridge is wholly exhausted, the cartridge is replaced for a new cartridge by an operator. Therefore, easy replacement work must be required in the sheet cartridge. Further, after assembly of the new cartridge and after installation of the image recording medium at the predetermined sheet path defined in the image recording apparatus, the installed image recording medium must be smoothly transferred along the sheet path, otherwise sheet slacking or jamming may occur.
With the above general matter in view, in the conventional sheet cartridge which accommodates therein the rolled image recording medium, a shielding member is provided at an opening of a cartridge casing for preventing the internal image recording medium from being exposed to light prior to the assembly of the cartridge into the image recording apparatus. Further, a leader portion is provided at a leading end portion of the image recording medium so as to properly direct the image recording medium in the sheet path of the image recording apparatus, and the leader portion is slightly protruded out of the opening for pulling the sheet out of the cartridge casing.
Further, in the conventional sheet cartridge a back tension or braking force is applied to the elongated image recording medium so as to provide a proper tension to the medium in traveling along the sheet path. Therefore, in the sheet cartridge prior to the assembly into the apparatus, the leader portion is provided with a locking pawl which prevents the protruded leader portion from being retracted into the cartridge casing. When the leader tape is wound over the takeup shaft, the subsequent image recording medium can not be further retracted into the sheet cartridge casing. Thereafter, a mechanism for removing the locking pawl is actuated, so that the locking pawl is out of contact with the image recording medium.
With such a conventional sheet cartridge, after assembly of the sheet cartridge into the apparatus, the light shielding member must be removed. In this case, since the back tension is applied to the rolled image recording medium, the protruded leader portion must be manually gripped so as to prevent the medium from being retracted into the cartridge casing. Therefore, smooth handling to the sheet cartridge may not be attainable in the conventional cartridge. If the operator erroneously releases the external leader portion, the leader portion may be retracted into the casing due to the applied back tension. If the cartridge is intended to be used, the cartridge must be subjected to disassembly in a dark room.
Further, in the conventional image recording medium using the elongated image recording medium accommodated in
the sheet cartridge, the cartridge is simply mounted at a proper location in the apparatus, and neither means for fixing the cartridge at a position nor means for releasing the fixing means are provided in the apparatus. Therefore, the operator can easily remove the cartridge from the apparatus. However, when the cartridge is removed from the image recording apparatus while non-used image recording medium is still rolled in the sheet cartridge, the mechanism for releasing the locking pawl is rendered inoperable, and the free locking pawl may be brought into contact with the image recording medium, to thereby damage an image recorded thereon.
As described above, the image recording medium in the sheet cartridge is subjected to back tension or a braking force so as to provide a proper tension to the medium when it is running along the sheet path. More specifically, the elongated image recording medium is wound over a supply shaft extending through the cartridge casing, and a frictional braking force is applied to the shaft. In this case, if a low frictional force is applied, sheet overrunning may occur due to inertial force of the sheet roll. Therefore, sheet slacking may occur in the sheet path, and image recording operation may be degraded. On the other hand, if excessive frictional force is applied to the supply shaft, the image recording medium may be torn or cut due to excessive tension applied thereto. To avoid this problem, in the conventional sheet cartridge, the size of the cartridge casing and the flanges of the supply shaft are precisely determined, so as to provide a substantially constant frictional force between the casing and the flange.
However, it would be rather difficult to provide such casing and flanges having high dimensional accuracy, and dimensional error may lead to the non-uniformity of the frictional force. As a result, improper imaging may be provided and yieldability may be lowered.
In still another aspect in the conventional image recording apparatus, the image recording medium is traveled along the sheet path defined by sheet transferring means such as sheet feed rollers. The image recording medium sup plied from the sheet cartridge is directed toward an exposure zone and a pressure developing unit by means of rollers. However, during this transfer, if dust or foreign objects attached to the surface of the image recording medium is transferred or translated into a peripheral surface of the feed roller and the transferred dust is deposited thereon, the coefficient of friction provided by the roller surface may be changed, and accordingly, the image recording medium is not smoothly delivered toward the exposure zone and the pressure developing unit. Consequently, multiple light exposures may occur, or a distance between the neighboring images on the recording medium may be improperly elongated. Further, if the image recording medium in the cartridge is a photosensitive pressure sensitive recording medium, it would be almost impossible to provide a proper positional alignment with a developer medium at the pressure developing unit, and the resultant output image may be degraded.
In another aspect in the conventional image recording apparatus, if the sheet transferring means is operated while the rotation of the takeup shaft is terminated or suspended, a sheet slack occurs at a sheet path portion immediately upstream of the takeup means. If such slackened sheet medium is again involved in the rotating rollers, sheet jamming may occur. Normally, such sheet jamming cannot be easily cleared by simply pulling the sheet medium. To correct this jamming, the image recording apparatus must be disassembled, and the jammed sheet cut into pieces, and the rollers involving the jammed sheet must be removed. For an ordinary operator, it would be rather difficult to deal with such sheet jamming.